1. Field of the Invention
The present invention relates to a wireless access system, and more particularly, to a method and apparatus for performing a plurality of network attachment procedures to support a plurality of connections for a small cell-based User Equipment (UE) service.
2. Discussion of the Related Art
Wireless access systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless access system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
Recently, a wireless access network configuration has been changed such that various types of small cells having small sizes such as a pico cell, a femto cell, etc. interact with a macro cell having a relatively large size. The wireless access network configuration aims to provide a high data rate to final UEs and thus increase Quality of Experience (QoE) for the final UEs in a situation where multi-layer cells co-exist in a hierarchical structure basically involving a macro cell.
According to one of the current 3rd Generation Partnership Project (3GPP) standardization categories, Small Cell Enhancements for E-UTRA and E-UTRAN SI; e.g., RP-122033, enhancement of indoor/outdoor scenarios using low-power nodes is discussed under the title of small cell enhancement. In addition, scenarios and requirements for the small cell enhancement are described in 3GPP TR 36.932.
Considering the development trend, a larger number of smaller cells will be deployed within macro cells and thus final UEs will be located physically nearer to a network. Accordingly, it is expected that communication will be conducted through UE-based zones in a future-generation wireless access network, instead of conventional physical cell-based communication. To realize communication through UE-based zones with the aim of increasing throughput, technical issues should be handled to provide a service providing unit such as a UE zone, different from a conventional service providing unit such as a physical cell. The emergence of these small cells may significantly affect a current Remote Area Network (RAN).
According to 3GPP TS 36.300, a cell is basically composed of downlink resources and optional uplink resources. Linkage between the carrier frequencies of the downlink resources and the carrier frequencies of the uplink resources is indicated by System Information (SI) transmitted in downlink resources.
According to 3GPP TS 23.401, if a UE is to receive a service requiring registration, the UE should register to a network. The registration procedure is referred to as network attachment. During the network attachment, an evolved Node B (eNB or eNode B) and/or the UE establishes an Evolved Packet System (EPS) bearer, thereby enabling ‘Always on Internet Protocol (IP) connectivity’ for the UE. In the network attachment procedure, one or more dedicated bearer establishment operations may be triggered to establish dedicated EPS bearers for the UE. In addition, the UE may request allocation of an IP address during the network attachment.
Considering a future high-density small cell deployment scenario, UE-based zone configuration will be a significant issue. Accordingly, a current network attachment procedure needs to be improved to support UE-based zone configuration.